In recent years, various types of information have been stored in information devices along with pervasive use of the information devices. As a result of this, establishment of a security technology of suppressing a leakage of information stored in the information device has become a very important issue, and various authentication techniques (for example, password authentication, biometric authentication, and card authentication) have been proposed. However, since most of existing authentication techniques perform authentication processing only at a time of login, in the case where an unauthorized person illegally uses an information device while an authorized user steps away from the information device, there is a common problem in which it is not possible to detect illegal use.
In order to solve the problem, a continuous authentication technique in which processing is continuously performed to authenticate a post-login user, has been proposed. As representative continuous authentication, there is continuous authentication due to face authentication using a feature vector. In the face authentication, the continuous authentication is executed such that a characteristic point group as a feature vector group in a face region corresponding to a monitored user is registered, and the user is recognized based on correlation between the registered characteristic point group and a characteristic point group which is extracted when performing authentication.
In addition, a color histogram authentication in which a color histogram of an image of a user is used has also been proposed. The color histogram authentication has an advantage in which robust continuous authentication is possible with respect to a change in posture of a user, compared to another method using the face authentication or the like. In the color histogram authentication, the continuous authentication is executed, for example, by registering a color histogram of a region (for example, body region) corresponding to a user in an image, detecting the body region of the user in the image based on a similarity of the registered color histogram and an imaged color histogram, and by tracking a movement thereof. As a technique related to such image processing, for example, documents of F. Monrose and A. D. Rubin, “Keystroke dynamics as a biometric for authentication,” Future Generation Comput. Syst., vol. 16, pp. 351-359, 2000., A. Altinok and M. Turk, “Temporal integration for Continuous Multimodal Biometrics,” in Proc. Workshop on Multimodal User Authentication, 2003, pp. 131-137., T. Sim, S. Zhang, R. Janakiraman, and S. Kumar, “Continuous Verification Using Multimodal Biometrics,” IEEE Trans. Pattern Anal. Mach. Intell., vol. 29, no. 4, pp. 687-700, April 2007., and K. Niinuma, U. Park, A. K. Jain, “Soft Biometric Traits For Continuous User Authentication”, IEEE Transactions on Information Forensics and Security (TIFS), Vol. 5, No. 4, pp. 771-780, 2, 2010. are disclosed.